Audacity(r) needs a plugin called "Lame" to export to mp3 format. It also uses the "FFmpeg" plugin to be able to read/import mp4 files, too. My site, lame.buanzo.org, provides
versions for Windows and Mac OSX of those plugins. There are more details on my site. Please, read before clicking. That is good internet advice. There are ads on my site, and even though we block the malware ones (with your help, my email address is available on site), the malware ads come from a MALWARE INDUSTRY. Ads are good, they help me maintain this free service, and there are MILLIONS of awesome products and services advertised, but please, stay away from 'click here download now' banners!